Battery charger with temperature control

ABSTRACT

A battery charging circuit monitors the IC temperature through monitoring the charging die temperature, or directly monitoring the IC temperature using a temperature sensor. A maximum temperature allowed for the charging die is predetermined. The charging circuit is capable of reducing charging current at the predetermined maximum temperature value. The charging die signal is compared by a reference signal to achieve the reduction of charging current at the maximum allowed temperature value.

1. FIELD OF THE INVENTION

The invention is related to a battery charger, more specifically to abattery charger circuit that is capable of monitoring and adjusting thecharging die temperature to prevent the integrated circuit (“IC”) fromoverheating during the charging of the battery.

2. DESCRIPTION OF THE RELATED ART

It is a common experience that when charging a battery, the IC tends toheat up during the charging of the battery. The heat during the chargingis caused by the IC power consumption, mostly by the charging current.When the charging current is reduced, the heat is usually reduced. Overthe years there have been many attempts to control the charging currentin order to obtain an optimal value to achieve effective charging andprevent overheating at the same time. Some of these attempts were provento be either too complicated or too expensive. Because most of therechargeable batteries are used in consumer electronic products, thecost of the charging IC is a big concern for the electronicsmanufacturers. The present invention introduces an effective and aninexpensive circuit and a method to achieve the purposes of botheffective charging and overheating prevention.

SUMMARY OF THE INVENTION

The invention is a battery charging circuit that monitors IC temperaturethrough monitoring the charging die temperature, or directly monitoringthe IC temperature, using a temperature sensor with a predeterminedmaximum temperature value and a circuit that reduces charging current atthe predetermined maximum temperature value to achieve the purpose ofpreventing the IC temperature from exceeding the maximum allowedtemperature value.

Although the primary application of this invention is for the control ofthe temperature of the charging die and maintaining the charging ICtemperature under the predetermined maximum value, it can also be usedfor other types of ICs for the control of their temperatures.

In one embodiment of the invention, a circuit for charging a batterycomprises a charging current loop providing charging current to thebattery where the charging current varies with a reference voltage, anda control loop capable of adjusting the reference voltage according to acharging die temperature. When the charging die temperature exceeds apreset temperature threshold, the charging current is reduced byreducing the reference voltage through the control loop.

In another embodiment of the invention, a present invention is a methodfor charging a battery comprising providing charging current through acharging circuit to the battery where the charging current varies with areference voltage and adjusting the reference voltage through a controlcircuit according to a charging die temperature.

When the charging die temperature exceeds a preset temperaturethreshold, the charging current is reduced by reducing the referencevoltage through the control loop.

In yet another embodiment of the invention, a method is described forcharging a battery comprising providing charging current through acharging circuit to the battery where the charging current varies with areference voltage and adjusting the reference voltage through a controlcircuit according to a temperature of an integrated circuit thatcontains the charging circuit and the control circuit. When thetemperature of the integrated circuit exceeds a preset temperaturethreshold, the charging current is reduced by reducing the referencevoltage through the control loop.

BRIEF DESCRIPTION OF THE DRAWING

These and other features, aspects and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying figure where:

FIG. 1. is a schematic diagram of a battery charging circuit accordingto embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The purpose of this invention is to monitor the charger IC'stemperature. When the temperature of the charger IC is over a certainpredetermined value, the temperature of the IC will be reduced by thecircuit described in this invention. The following describes a method bywhich this is accomplished.

The die temperature indication (DTI) 10 shown in FIG. 1 indicates thetemperature on the charging die. This is commonly accomplished by atemperature sensor that provides a voltage signal Vdt 20 to one of theinputs of the amplifier 30 as one of the references. The voltage signalVdt 20 can also be obtained through a temperature sensor which monitorsthe temperature directly from the IC. The other input of the amplifier30 is connected to a reference voltage Vref 40 through R1 50 as anotherreference to the amplifier 30. The reference voltage Vref1 60 isconnected to Vref 40 through the resistor R1 50. The Vref 40 is suppliedby the Vref1 60 using R1 50 as a divider to divide the portion of theVref1 60 to the Vref 40. Vref1 60 is a constant source with a presetvalue and Vdt 20 is a function of die temperature. Therefore, Vref 40 isdependent from the charging die temperature, or the IC temperature.

As the temperature of the charging IC rises, the output voltage, Vdt 20,of the DTI 10 increases. When the die temperature rises to apredetermined temperature, i.e. Vdt 20 reaches a preset value, the dietemperature will, according to the circuit of the present invention,start to decrease. This process of decreasing the die temperature isillustrated as follows:

When the die temperature is higher than the predetermined value, Vdt 20is higher than Vref1 60. MOS 70 is a switch and when MOS 70 is open,Vref 40 is about half of Vref1 60. When the voltage value of Vdt 20 ishigher than the preset voltage value of Vref1 60, switch MOS 70 closes.When MOS 70 is closed, the resistor R2 80 is shorted out. In turn, Vref40 decreases. As illustrated by the following equation:

I1 90=Vx 100/Rc 110

when Vref 40 decreases, I1 90 decreases. In turn, when I1 90 decreases,I 120 also decreases. Therefore, when Vref 40 decreases, the chargingcurrent I 120 will also decrease.

The charging current I 120 has a direct effect to the die temperature,or the IC temperature, because the heat source of the die temperature isthe charging current. The heat source of the die temperature isgenerated by the charging current I 120 and the voltage drop ΔV 130 atthe Q2 140 during charging of the battery. I.e. The heat source=I 120×ΔV130. Therefore, when the charging current I 120 is decreased, the amountof the heat generated is decreased, so that the temperature on thecharging die is also decreased.

Vin 150 is the power source for the charger supplied by the AC adaptor.Q1 160 and Q2 140 are charging a pass device for the charger. The output(the collector) of Q2 140 is connected to the charging battery 170.

Iout 180 is the output current that is applied to the charging battery170.

Iout 180=Vref 40×K/Rc 110; where K is a design constant.

The choice of a temperature sensor is not a critical criterion inpracticing the present invention, although different temperature sensorscould generate different voltage values. To practice the invention, thepredetermined reference value Vref1 60 can be adjusted to obtain a bestvalue that is appropriate for the selected temperature sensor.

EXAMPLE

The maximum die temperature is set at 120° C.

Select a temperature sensor with the condition that when the dietemperature is at 120° C., the Vdt is at 1.0 V; and that when the dietemperature is at 0° C., the Vdt is at 1.35 V.

Vref1 is set at 1.0 V constant.

When the die temperature reaches 121° C. during the charge of thebatteries, the Vdt is at 0.95 V; the MOS switch is on; Vref decreases;Vx decreases; I1 decreases (I1=Vx/Rc) and finally I decreases. Becausethe charging current decreases, the die temperature also decreases.

Although the present invention has been discussed in considerable detailwith reference to certain preferred embodiments, other embodiments arepossible. Therefore, the scope of the appended claims should not belimited to the description of preferred embodiments contained in thisdisclosure.

1-20. (canceled)
 21. A battery charger integrated circuit withtemperature control, comprising: a temperature sensor circuit,electrically coupled to receive a first reference voltage (VREF1) and atemperature reading voltage (VDT), operable to generate a secondreference voltage (VREF) that is related to said first reference voltage(VREF1), wherein whenever said temperature reading voltage (VDT)surpasses said first reference voltage, said temperature sensor circuitis operable to adjust said second reference voltage (VREF); and acharging current generator circuit, electrically coupled to receive saidsecond reference voltage (VREF), operable to generate and continuouslyadjust a reference current (I1) and a charging current (I) according tosaid second reference voltage (VREF).
 22. The battery charger integratedcircuit of claim 21 wherein temperature sensor circuit further comprisesa die temperature indicator, connected to said battery chargerintegrated circuit, operable to generate a current that is proportionalto a temperature measurement of said battery charger integrated circuit.23. The battery charger integrated circuit of claim 22 wherein saidtemperature reading voltage (VDT) is linearly proportional to saidcurrent.
 24. The battery charger integrated circuit of claim 23 whereinsaid second reference voltage (VREF) is linearly proportional to saidfirst reference voltage (VREF1) and when said temperature readingvoltage (VDT) surpasses said first reference voltage (VREF1), saidtemperature sensor circuit is operable to reduce said second referencevoltage (VREF) so that said charging current is reduced.
 25. The batterycharger integrated circuit of claim 24 wherein said temperature sensorcircuit further comprises: an error amplifier, electrically coupled tosaid first reference voltage (VREF1) and said temperature sensingvoltage (VDT), operable to generate a logic output signal, whenever saidtemperature sensing voltage (VDT) surpasses said first reference voltage(VREF1), said error amplifier generates said logic output signal toadjust said second reference voltage (VREF); and a n-channel Metal OxideSemiconductor (nMOS) switch transistor, electrically coupled to receivesaid logic output signal from said error amplifier; and a resistivedivider circuit, electrically coupled to said first reference voltage(VREF1), said second reference voltage (VREF), and said nMOS switchtransistor, operable to establish a linear relationship between saidfirst reference voltage (VREF1) and said second reference voltage(VREF).
 26. The battery charger integrated circuit of claim 21 whereinsaid charging current generator circuit further comprises: a seconderror amplifier, electrically coupled to receive said second referencevoltage (VREF), operable to generate a second logic output signal,whenever said second reference signal (VREF) chances due to saidtemperature measurement increases, said second error amplifier isoperable to issue said second logic output signal; and a current mirrorcircuit, electrically coupled to said second error amplifier, operableto generate said reference current and said charging current.
 27. Thebattery charger integrated circuit of claim 26 wherein said currentmirror circuit further comprises: A first npn bipolar junctiontransistor; and A second npn bipolar junction transistor, the emitter ofsaid second npn transistor is electrically coupled to the emitter ofsaid first npn transistor and to an input voltage (VIN), the base ofsaid second npn electrically connected to the base of said first pnptransistor and to the collector of said first pnp transistor.
 28. Thebattery charger integrated circuit of claim 27 wherein said currentmirror circuit further comprises: a second p-channel Metal OxideSemiconductor (MOS) transistor, electrically coupled to receive saidsecondlogic output signal from said second error amplifier, said secondnMOS transistor electrically coupled to a current reference generatorcircuit electrically coupled to said second nMOS transistor operable togenerate said reference current whenever said second nMOS transistor isturned ON by said second error amplifier.
 29. The battery chargerintegrated circuit of claim 28 wherein said reference current generatorcircuit further comprises: A voltage source; and A resistor,electrically coupled to said voltage source, said second nMOStransistor, and said second error amplifier.
 30. The battery chargerintegrated circuit of claim 21 wherein temperature sensor circuitfurther comprises a die temperature indicator, connected to said batterycharger integrated circuit, operable to generate a current that isinversely proportional to a temperature measurement of said batterycharger integrated circuit and wherein temperature reading voltage (VDT)varies linearly proportionally with said current.
 31. The batterycharger integrated circuit of claim 30 wherein said second referencevoltage (VRED) is linearly proportional to said first reference voltage(VREF1) and when said temperature reading voltage (VDT) surpasses saidfirst reference voltage (VREF1), said temperature sensor circuit isoperable to reduce said second reference voltage (VREF) so that saidcharging current is reduced.
 32. The battery charger integrated circuitof claim 21 wherein said charging current generator circuit is poweredby an input voltage (VIN).
 33. A method of providing temperature controlin a battery charger integrated circuit, comprising: providing atemperature reading voltage (VDT) representative of a temperaturemeasurement of said battery charger integrated circuit; providing asecond reference voltage (VREF) related to said first reference voltage(VREF); and comparing said temperature reading voltage (VDT) to a firstreference voltage (VREF1), whenever said temperature reading voltage(VDT) surpasses said first reference voltage (VREF1), adjusting saidsecond reference voltage (VREF) so as to adjust a charging current thatis proportional to said temperature measurement.
 34. The method of claim33 wherein said providing a temperature reading voltage furthercomprises: taking said temperature measurement of said battery chargerintegrated circuit from a die temperature indicator; and converting saidtemperature measurement into said temperature reading voltage.
 35. Themethod of claim 33 wherein said temperature reading voltage is linearlyproportional to said temperature measurement.
 36. The method of claim 33wherein said temperature reading voltage is inversely proportional tosaid temperature measurement.
 37. The method of claim 36 wherein saidcomparing said temperature reading voltage to said first referencevoltage further comprises: generating a logic output signal so as toadjust said second reference voltage; using said logic output signal togenerate a reference current; and using said reference current togenerate said charging current that is linearly proportional to saidreference current and to said second reference voltage (VREF).
 38. Abattery charger integrated circuit with temperature control, comprising:means for generating a second reference voltage upon receiving atemperature reading voltage and a first reference voltage; and means foradjusting a charging current based on said second reference voltagewhich is based on said first reference voltage so as to maintain saidtemperature reading voltage below said first reference voltage.
 39. Thebattery charger integrated circuit of claim 38 wherein said secondreference voltage generating means further comprises: means forcomparing said temperature reading voltage to said first referencevoltage, whenever said temperature reading voltage surpasses said firstreference voltage, said comparing means continuously adjusting saidsecond reference voltage so as to adjust said charging current that isproportional to said temperature measurement.
 40. The battery chargerintegrated circuit of claim 39 wherein said comparing means furthercomprises: a resistive network for establishing a linear relationshipbetween said first reference voltage and said second reference voltage;and transistor means, electrically coupled between said comparing meansand said value establishing means, for continuously changing therelationship between said first reference voltage and said secondreference voltage in said resistive network.
 41. The battery chargerintegrated circuit of claim 38 wherein said charging current adjustingmeans further comprises: means, electrically coupled to said comparingmeans, for generating said charging current based on a referencecurrent, wherein upon receiving said second reference signal, saidcharging current generating means operates to adjust said referencecurrent so as to adjust said charging current.